Direct Allylation of In Situ Generated Aldehyde Acyl Anions by Synergistic NHC and Palladium Catalysis

The direct regioselective allylation of in situ generated aldehyde acyl anions has been achieved by synergistic NHC and Pd catalysis. It provides an efficient access to valuable β,γ‐unsaturated ketones under mild reaction conditions starting from easily accessible allylic carbonates and aldehydes without any preactivation. The synergistic catalysis method demonstrated herein adds a new dimension to the area of metal‐mediated C allylation.     

Dehydrative Allylation between Aldehydes and Allylic Alcohols through Synergistic N-Heterocyclic Carbene/Palladium Catalysis

Dehydrative allylation between widely available aldehydes and allylic alcohols to afford β,γ-unsaturated ketones was enabled by a synergistic merger of a thiazolium N-heterocyclic carbene catalyst and a palladium-bisphosphine catalyst.     

Modular In Situ Functionalization Strategy: Multicomponent Polymerization by Palladium/Norbornene Cooperative Catalysis

Herein, we report a cooperatively palladium/norbornene‐catalyzed polymerization, which simplifies the synthesis of functional aromatic polymers, including conjugated polymers. Specifically, an A₂B₂C‐type multicomponent polymerization that is based on an ortho amination/ipso alkynylation reaction was developed for the preparation of various amine‐functionalized arylacetylene‐containing polymers. Within a single catalytic cycle, the amine side chains are site‐selectively installed in situ by C?H activation during the polymerization process, which represents a major difference from conventional cross‐coupling polymerizations. This “in situ functionalization” strategy enables the modular incorporation of functional side chains starting from simple monomers, thereby conveniently affording a diverse range of functional polymers.     

Oxidative Addition of 2‐Halogenoazoles—Direct Synthesis of Palladium(II) Complexes Bearing Protic NH,NH‐Functionalized NHC Ligands

The chemistry of N‐heterocyclic carbenes (NHCs) is dominated by N,N′‐dialkylated or ‐diarylated derivatives. Such NHC ligands are normally obtained by C2‐deprotonation of azolium cations or by reductive elimination from azol‐2‐thiones. A simple one‐step procedure is described that leads to complexes with NH,NH‐functionalized NHC ligands by the oxidative addition of 2‐halogenoazoles to complexes of zero‐valent transition metals.     

Direct Catalytic Addition of Alkylnitriles to Aldehydes by Transition‐Metal/NHC Complexes

Direct catalytic addition of alkylnitriles to aldehydes allows for an atom‐economical access to β‐hydroxynitriles under proton transfer conditions. Direct use of alkylnitriles as pronucleophiles has been hampered due to their low acidity resulting in an inability to generate α‐cyano carbanions in a catalytic manner. A transition metal/N‐heterocyclic carbene (NHC) complex prepared from [{Rh(OMe)(cod)}₂] and an imidazolium‐based carbene was identified as an effective catalyst to promote the reaction with as little as 1.25 mol % of catalyst loading. The corresponding Rh complex, derived from chiral triazolium salt, rendered the reaction enantioselective, albeit with moderate enantioselectivity.     

Enantioselective Desymmetrization of Cyclobutanones Enabled by Synergistic Palladium/Enamine Catalysis

The enantioselective intramolecular α‐arylation of cyclobutanones has been established by combining palladium and enamine catalyst systems. Two different enantioselective control strategies have been developed for cyclobutanone substrates bearing O‐ or N‐tethered aryl bromides. Further synthetic applications are also reported.     

The Development of Bulky Palladium NHC Complexes for the Most-Challenging Cross-Coupling Reactions

Palladium‐catalyzed cross‐coupling reactions enable organic chemists to form C? C bonds in targeted positions and under mild conditions. Although phosphine ligands have been intensively researched, in the search for even better cross‐coupling catalysts attention has recently turned to the use of N‐heterocyclic carbene (NHC) ligands, which form a strong bond to the palladium center. PEPPSI (pyridine‐enhanced precatalyst preparation, stabilization, and initiation) palladium precatalysts with bulky NHC ligands have established themselves as successful alternatives to palladium phosphine complexes. This Review shows the success of these species in Suzuki–Miyaura, Negishi, and Stille–Migita cross‐couplings as well as in amination and sulfination reactions.     

Copper/Palladium Synergistic Catalysis for the syn‐ and anti‐Selective Carboboration of Alkenes

A method for the diastereoselective carboboration of 1,2‐disubstituted styrenes with aryl/vinyl bromides and (Bpin)₂ is reported. High diastereoselectivities and yields are observed for the formation of either diastereomer of the product from a single alkene isomer. These reactions provide access to a diverse range of structures from simple starting materials.     

A Remarkably Simple Hybrid Surfactant–NHC Ligand,Its Gold‐Complex,and Application in Micellar Catalysis

A combination of an N‐heterocyclic carbene (NHC) ligand and a structurally simple surfactant has been realized, the hybrid surfactant–NHC. The related gold complex was synthesized, fully characterized, and applied in catalysis. This remarkably simple strategy allows, in combination with a co‐surfactant, the application of gold catalysis in water.     

Large yet Flexible N‐Heterocyclic Carbene Ligands for Palladium Catalysis

A straightforward and scalable eight‐step synthesis of new N‐heterocyclic carbenes (NHCs) has been developed from inexpensive and readily available 2‐nitro‐m‐xylene. This process allows for the preparation of a novel class of NHCs coined ITent (“Tent” for “tentacular”) of which the well‐known IMes (N,N′‐bis(2,4,6‐trimethylphenyl)imidazol‐2‐ylidene), IPr (N,N′‐bis(2,6‐di(2‐propyl)phenyl)imidazol‐2‐ylidene) and IPent (N,N′‐bis(2,6‐di(3‐pentyl)phenyl)imidazol‐2‐ylidene) NHCs are the simplest and already known congeners. The synthetic route was successfully used for the preparation of three members of the ITent family: IPent (N,N′‐bis(2,6‐di(3‐pentyl)phenyl)imidazol‐2‐ylidene), IHept (N,N′‐bis(2,6‐di(4‐heptyl)phenyl)imidazol‐2‐ylidene) and INon (N,N′‐bis(2,6‐di(5‐nonyl)phenyl)imidazol‐2‐ylidene). The electronic and steric properties of each NHC were studied through the preparation of both nickel and palladium complexes. Finally the effect of these new ITent ligands in Pd‐catalyzed Suzuki–Miyaura and Buchwald–Hartwig cross‐couplings was investigated.     

Catalytic C(sp3)−H Arylation of Free Primary Amines with an exo Directing Group Generated In Situ

Herein, we report the palladium‐catalyzed direct arylation of unactivated aliphatic C?H bonds in free primary amines. This method takes advantage of an exo‐imine‐type directing group (DG) that can be generated and removed in situ. A range of unprotected aliphatic amines are suitable substrates, undergoing site‐selective arylation at the γ‐position. Methyl as well as cyclic and acyclic methylene groups can be activated. Furthermore, when aniline‐derived substrates were used, preliminary success with δ‐C?H arylation was achieved. The feasibility of using the DG component in a catalytic fashion was also demonstrated.     

Synergistic N‐Heterocyclic Carbene/Palladium‐Catalyzed Reactions of Aldehyde Acyl Anions with either Diarylmethyl or Allylic Carbonates

Benzylation and allylation of aldehyde acyl anions were enabled by the merger of a thiazolium N‐heterocyclic carbene (NHC) catalyst and a palladium/bisphosphine catalyst in a synergistic manner. Owing to the mildness of the reaction conditions, various functional groups were tolerated in the substrates.     

Synthesis of 3,3‐Disubstituted Oxindoles by Palladium‐Catalyzed Asymmetric Intramolecular α‐Arylation of Amides: Reaction Development and Mechanistic Studies

Palladium complexes incorporating chiral N‐heterocyclic carbene (NHC) ligands catalyze the asymmetric intramolecular α‐arylation of amides producing 3,3‐disubstituted oxindoles. Comprehensive DFT studies have been performed to gain insight into the mechanism of this transformation. Oxidative addition is shown to be rate‐determining and reductive elimination to be enantioselectivity‐determining. The synthesis of seven new NHC ligands is detailed and their performance is compared. One of them, L8 , containing a tBu and a 1‐naphthyl group at the stereogenic centre, proved superior and was very efficient in the asymmetric synthesis of fifteen new spiro‐oxindoles and three azaspiro‐oxindoles often in high yields (up to 99 %) and enantioselectivities (up to 97 % ee; ee=enantiomeric excess). Three palladacycle intermediates resulting from the oxidative addition of [Pd(NHC)] into the aryl halide bond were isolated and structurally characterized (X‐ray). Using these intermediates as catalysts showed alkene additives to play an important role in increasing turnover number and frequency.     

钯配合物和手性磷酸连续催化的烯丙醇和醛的不对称羰基烯丙基化反应

利用钯配合物/手性磷酸催化剂体系,通过不对称连续催化,实现了烯丙醇和醛的不对称羰基烯丙基化反应.该反应使用廉价易得的烯丙醇底物,在催化量的手性磷酸作用下,以优秀的产率和立体选择性得到了高烯丙醇产物.